A computer is provided having a bus interface unit coupled between a CPU bus and a mezzanine bus, or PCI bus. The bus interface unit includes a plurality of input buffers which can be selectively connected and disconnected in a dynamic fashion according to active and inactive signals forwarded thereto. Signals forwarded to the bus interface unit from the CPU are classified according to the transaction phase of CPU bus activity. If signals associated with one particular transaction phase are active, then input buffers attributed to signals of other transaction phases can be deactivated. It is preferred that input buffers associated with signals of a request and arbitration phase be maintained active and coupled to power regardless of the present transaction phase unless the computer enters a powered down mode, such as sleep, idle or standby.